Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured so as to have a small size and weight if possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit cell) of the middle- or large-sized battery module. Especially, considerable interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
Battery cells constituting the middle- or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. If the heat, generated from the battery module during the charge and discharge of the battery module, is not effectively removed, the heat accumulates in the battery module, with the result that the deterioration of the battery module is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
Generally, a battery module, which is mounted in the middle- or large-sized battery pack, is manufactured by stacking a plurality of battery cells with high integration. The battery cells are stacked, such that neighboring battery cells are spaced apart from each other by a predetermined distance, to remove heat generated during the charge and discharge of the battery cells. For example, the battery cells may be sequentially stacked such that neighboring battery cells are spaced apart from each other by a predetermined distance without the use of additional members. When the battery cells have low mechanical strength, on the other hand, one or more battery cells may be mounted in a cartridge, and a plurality of cartridges, in each of which the battery cells are mounted, may be stacked to constitute a battery module. Coolant channels may be defined between stacked battery cells or between stacked battery modules to effectively remove heat accumulating between the battery cells or between the battery modules.
In this structure, however, it is necessary to provide a plurality of coolant channels corresponding to the plurality of battery cells, with the result that the overall size of the battery module increases.
Also, the more battery cells are stacked, the narrower the width of each of the coolant channel is, when considering the size of the battery module. As a result, it may be complicated to design a cooling structure. That is, the coolant channels having a width narrower than an inlet port of a coolant cause high pressure loss, with the result that there is great difficulty in designing the shape and position of inlet and outlet ports of the coolant. Also, a fan may be further installed to prevent such pressure loss. As a result, there are design restrictions in, for example, power consumption, fan noise, and space.
Furthermore, battery cells located at the middle of the battery cell stack may not be satisfactorily cooled, and may deteriorate more rapidly than the outermost battery cells. Such nonuniform deterioration of the battery cells may reduce service life of the battery module, which is not preferable in terms of safety.
Consequently, there is a high necessity for a battery module that provides high-power, large-capacity electric power, is manufactured in a simple and compact structure, and has excellent service life and safety characteristics.